Frequency demodulation apparatus incorporated in wideband frequency modulation systems typically utilizes delay line discrimination devices which employ double balanced mixers in combination with delay lines. Mixers have nonlinear signal transfer characteristics which have two adverse effects. In the first place the linearity of the mixer varies with frequency so that changes in bandwidth produce changes in linearity and vice versa. This is undesirable since bandwidth and the linearity cannot be selected independently of each other. Secondly, the sensitivity, or signal-to-noise ratio, of the device also varies with changes in bandwidth. This is also undesirable since sensitivity and signal-to-noise ratio cannot be selected independently of each other.
The present invention is directed toward a new type of demodulation system which is characterized by a significant reduction in nonlinear signal transfer characteristics and which enables wider bandwidth operation to be obtained than previously available for specified values of linearity and sensitivity or alternatively enables enhanced linearity and sensitivity to be obtained when bandwidths are not increased.